Chemistry - A European Journal
Chemistry - A European Journal
4 years ago

2-(Pyridinium-1-yl)-1,1-bis(perfluoroalkylsulfonyl)ethan-1-ide: A Practical Reagent for Synthesis of Strongly Acidic 1,1-Bis(perfluoroalkylsulfonyl)alkanes

2-(Pyridinium-1-yl)-1,1-bis(perfluoroalkylsulfonyl)ethan-1-ide: A Practical Reagent for Synthesis of Strongly Acidic 1,1-Bis(perfluoroalkylsulfonyl)alkanes
Akira Kotani, Takashi Matsumoto, Ryuta Takahashi, Hikaru Yanai, Hideki Hakamata, Yoichi Takahashi
On mixing (RfSO2)2CH2 (Rf=perfluoroalkyl), paraformaldehyde, and substituted pyridines, a three-component reaction proceeded smoothly to give unusual zwitterions bearing both pyridinium and stabilized carbanion moieties in good to excellent yields. Of these, 2-fluoropyridinium derivatives rapidly dissociated in acetonitrile to give equilibrium mixtures of the zwitterions and (RfSO2)2C=CH2/2-fluoropyridine, as confirmed by detailed variable-temperature NMR studies. The dynamic behavior of such 2-fluoropyridinium compounds allows them to be used as shelf-stable, easy-to-handle sources of (RfSO2)2C=CH2. With these reagents, strongly acidic carbon acids (RfSO2)2CHR were synthesized, which served as a new type of acid catalysts. Moreover, C−C bond-forming reactions with a ketene silyl acetal proceeded efficiently with Tf2C=CH2 generated in situ. Dropping acid: 2-Fluoropyridinium compounds, which were prepared from (RfSO2)2CH2 (Rf=perfluoroalkyl), paraformaldehyde, and 2-fluoropyridine, were developed as shelf-stable, easy-to-handle sources of (RfSO2)2C=CH2 (see scheme). By reaction of several nucleophiles with such reagents, superacidic carbon acids (RfSO2)2CHR were successfully synthesized.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/chem.201700515

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